The invention relates to a method and an apparatus for applying annular doses, in particular for forming an annular dose separating the annular dose from a continuous flow of plasticised material by means of an extruder and for applying the annular dose that has just been formed to a surface.
Specifically but not exclusively, the invention can be used for applying a seal to a surface, for example for forming gaskets on objects, for example inside capsules (made of metal or plastics) for closing containers. The invention can be further used to apply an annular dose to a flat element (for example a disc), made in particular of metal or plastics, which can then be inserted, as a seal, into a more complex device. It is possible, in other uses of the invention, to apply the annular dose (as a seal) to a carton element intended, for example, for forming a container or a portion of a container, or directly to a container, for example of plastics or metal.
The annular dose could also be inserted, according to another use of the invention, directly into a mould for obtaining an object therefrom (for example an annular object), in particular with closing functions (for example a cap consisting of a wall made of plastics and of a central metal disc provided with a gasket made from the annular dose) or also with functions other than closing functions.
The prior art comprises patent publication US 2012/0171381 A1 that shows an apparatus for forming an annular dose of plasticised material to be deposited on the surface of a capsule for containers to give rise to the sealing gasket. In this apparatus the dose is expelled and separated by virtue of the high closing speed of a mould that makes the material spurt out.
This known apparatus nevertheless has several limitations and drawbacks.
Firstly, the material that forms the annular dose is pressed out at high pressure, with a possible localised increase of the temperature and consequent deterioration of the material and/or adhesion of the material to the conduit surfaces.
Secondly, to press out the material, low viscosity must be maintained and it is thus necessary to work at relatively high temperatures.
Further, whereas on the one hand using high-viscosity material entails very high operating speeds, on the other hand using low-viscosity materials entails problems of the material running out from the seals.
Another drawback is that the annular dose, spurting out at high speed from the mould, can be deformed in a manner that is not easily controllable.
WO 97/18073 shows a method as in the preamble of claim 1.